Abstract
Although structural health monitoring (SHM) technologies using sensors have dramatically been developed recently, their capability should be evaluated from the perspective of the maintenance industry. As a first step toward utilizing sensors, the objective of the paper is to investigate the possibility of using sensors for inspecting the entire fuselage during C-check. First, we reviewed various sensors for their detection range, detectable damage size, and installed weight, which revealed that the piezoelectric wafer active sensor (PWAS) is the most promising sensor for aircraft SHM. Second, we performed a case study of inspecting the fuselage of Boeing-737NG using PWAS. To maintain the same detecting capability of manual inspection in C-check, we estimated the total number of sensors required. It turned out that utilizing sensors can reduce the maintenance downtime and thus, maintenance cost. However, even with a very conservative estimate, the lifetime cost was significantly increased due to the weight of sensor systems. The cost due to the weight increase was an order of magnitude higher than the cost saved by using SHM. We found that a large number of sensors were required to detect damage at unknown locations, which was the main cause of the weight increase. We concluded that to make SHM cost-effective, it would be necessary either to improve the current sensor technologies so that a less number of sensors are used or to modify the aircraft design concept for SHM.
Highlights
In the damage-tolerant design concept, aircraft are maintained for their safety and reliability using periodic maintenance
Structural maintenance of civil aviation aircraft is currently based on scheduled maintenance, where the maintenance interval is determined based on safety and reliability
The important criterion is the weight of structural health monitoring (SHM) systems, which includes the weight of the sensor itself and the weight of cables and connection ports. Both comparative vacuum monitoring (CVM) and fiber Bragg grating (FBG) have advantages in weight as they are composed of polymers, while piezoelectric wafer active sensor (PWAS) is heavier as it requires a metallic wire connection or metallic circuit in SMART Layer
Summary
In the damage-tolerant design concept, aircraft are maintained for their safety and reliability using periodic maintenance. We expect that the first step would be to replace manual inspection with SHM systems while the maintenance interval is still the same as scheduled maintenance This is the most probable scenario because non-structural maintenance, such as engine and avionics, can be performed at the same time. Even if there were prior publications that discussed the cost analysis for CBM [3], this is the first to consider sensor-based inspection of entire fuselage during the conventional C-check This is a transition state of CBM and can be a near-term implementation of SHM in the civil aviation industry.
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